Pressure-fluid-operated devices and means for indicating the condition thereof



B'QIO IEQO .s I'E FGR MISSING m Nov. 19, 1968 Filed Oct. 15, 1965 R. WARD 3,412,391 PRESSURE-FLUID-OPERATED DEVICES AND MEANS FOR INDICATING THE CONDITION THEREOF 6 Sheets-Sheet 1 I w- I Lo I l --J I N I I m I l 92 I I i' I T.'--I-T' II :I II}? J r I I4 9 I l l I I INVENTOR: RICHARD WARD Nov. 19, 1968- R. WARD 3,412,391

PRESSURE-FLUID-OPERATED DEVICES AND MEANS FOR INDICATING THE CONDITION THEREOF RICHARD MARD INVENTOR:

Nov. 19, 1968 R. WARD 3,412,391

PRESSURE-FLUID-OPERATED DEVICES AND MEANS FOR INDICATING THE CONDITION THEREOF Filed Oct. 15, 1965 6 Sheets-Sheet 5 RICHARD WA RD Nov. 19, 1968 R. WARD 3,412,391

PRESSURE'FLUIDOPERATED DEVICES AND MEANS FOR INDICATING THE CONDITION THEREOF Filed Oct. 15, 1965 6 Sheets-Sheet 4 RICHARD WARD INVENTOR:

NOV. 19, 1968 R 3,412,391

PRESSURE-FLUID-OPERATED DEVICES AND MEANS FOR INDICATING THE CONDITION THEREOF Filed Oct. 15, 1966 6 Sheets-Sheet INVENTOR:

R (CHARD WA RD Nov. 19, 1968 w 3,412,391

PRBSSURE-FLUID-OPERATED ICES AND MEANS FOR INDICATING THE CONDITION THEREOF Filed Oct. 15, 1965 6 Sheets-Sheet h TFF/ 171/ I INVENTOR:

RICHARD WRD MYS.

ABSTRACT OF THE DISCLOSURE A self-advancing mine roof support having a hydraulic ram member for advancing it and at least one hydraulically extensive prop member for securing it between floor and roof. The rarn member or the prop member or both have means for indicating, at a remote station, their extent of extension and retraction.

This invention is for improvements in or relating to selfadvancing mine roof supports of the kind having a hydraulic ram member for advancing the support and at least one hydraulically extensible prop. One object of the invention is to provide a system for indicating at a remote station the amount of extension of the hydraulic ram and/or hydraulic prop of the support.

According to thepresent invention there is provided a self-advancing mine roof support having a hydraulic ram member for advancing it land at least one hydraulically extensible prop member for securing it between floor and roof, at least one of said members being combined with means for indicating its extension and retraction comprising a cylinder, a piston within said cylinder, means for entry and exit of a pressure-fluid to and from the cylinder, at least one electric current conduction control element within said cylinder, means isolating said control element from pressure-fluid within the cylinder, means for varying the current conduction of said control element, and magnetic means responsive to relative movement of said piston and cylinder to adjust said control element varying means.

Some particular embodiments of the invention will now be described, by way of example, with reference to the accompanying semi-diagrammatic drawings in which:

FIGURE 1 is a side elevation of a form of self-advancing mine roof support to which the present invention is particularly, although not exclusively applicable,

FIGURE 2 is a fragmentary longitudinal sectional view of a hydraulic ram incorporated in the support shown in FIGURE 1 and adapted to push over the conveyor towards the coal face and then advance the support up to the conveyor,

FIGURE 3 is a fragmentary cross-section, to a larger scale, through the ram piston shown in FIGURE 1,

FIGURE 4 is a diagram showing the electrical connections of the potentiometer incorporated in the ram shown in FIGURES 2 and 3, for the purpose of the invention, and the manner in which this potentiometer may be connected in a remote indicating system,

FIGURES 5, 6, 7 and 8 are fragmentary longitudinal sectional views of four further embodiments of the invention as applied to a hydraulic ram or the like,

FIGURE 9 shows the electrical circuit for the embodiments of the invention shown in FIGURES 6, 7 and 8, and

3,4i238l Patented Nov. 19, 1968 FIGURE 10 shows a still further embodiment of the invention as applied to a hydraulic ram or the like.

Referring first to FIGURE 1 of the drawings, briefly, the mine roof support comprises a rear unit 10 and a forward unit 11.

The rear unit 10 comprises a base 12 on which are mounted four telescopic hydraulically extensible props 13, these props being arranged in side-by-side pairs at the front and rear of the base 12.

At their upper parts the hydraulic props or legs 13 support a roof-bar structure or canopy 14.

Mounted and secured in the base 12 of the rear support 10 is the cylinder of a hydraulic double-acting ram 15 having a forwardly extending piston rod 16.

The forward support unit 11 comprises a base 17 on which is mounted a single telescopic hydraulically extensible prop or leg 18 which, at its upper part, supports a cantilever roof-bar member 14a pivotally attached to the rear roof-bar structure or canopy 14 at 19.

The rear unit 10 and the front unit 11 are articulated together at their lower parts by a link 20 pivotally at tached to the rear unit at 21 and to the front unit at 22.

The piston rod 16 of the ram 15 has an extension or relay bar 23 which passes freely through the base 17 of the forward unit and is attached at 24 to the conveyor C. The conveyor C is arranged to carry away the coal as it is mined from the coal face in the usual way of longwall mining.

As winning of the coal from the coal face proceeds the ram 15, 16, 23 is extended so as to push the conveyor C towards the newly exposed coal face ready for a further traverse of said face by the coal cutting machine. When the conveyor has been pushed over the legs 13 and 18 of the support are lowered so as to release the roof-bar structure 14, 14a from the roof and the ram 15, 16 is then retracted so that, using the conveyor as an anchorage, the support is advanced up to the conveyor. The legs 13 and 18 are then extended again so as to secure the support firmly between floor and roof.

The hydraulic ram shown in FIGURES 2 and 3 of the drawing comprises a cylinder 25, having pressurefiuid entry and exit poi-ts 25a and 25b, and a ram proper having a piston 26 and a piston rod 27 which may conform structurally and functionally to the cylinder 15 and ram 16 of FIGURE 1 or may differ therefrom when utilized in the same or a different application.

The piston rod 27 is of tubular construction and houses a tube 28 of non-magnetic material. The tube 28 is sealed at both ends so as to isolate its interior from the pressurefiuid in the ram cylinder.

Enclosed within the tube 28 is a rectilinear potentiometer comprising a rod or bar 29 of insulating material which carries a resistance element or track 30, a slider track 31 of electrical conducting material and a return conduc' tor 32.

Mounted on the rod 29 for movement therealong is a wiper assembly 33 having a sprung brush or slider 34 adapted to traverse and make contact with the resistance element 30 and a sprung brush or slider 35 adapted to traverse and make electrical contact with the slider track 31. The brushes or sliders 34 and 35 are electrically con=- nected together.

The three connections of the potentiometer transducer just described are taken through insulating bushes 36 at one end of the ram cylinder and provided with terminals 37 (see FIGURE 4) for connecting the potentiometer transducer in the remote indicating system which, in the arrangement shown in FIGURE 4, comprises an electricity 3 supply source 38, a Wheatstone bridge circuit 39 and a current or potential responsive indicating instrument 40.

Movement of the wiper assembly 33 and thereby adjust ment of the potentiometer device is effected in accordance with the movement of the ram member 26, 27 by a magnetic coupling comprising a ring magnet 41, secured to the piston 26 and slidable over and along the exterior of the tube 28, and a ring armature 42 of iron or other ferromagnetic material, slidable within the bore of the tube 28 and to which the wiper assembly 33 is attached.

As the piston moves along the cylinder, carrying magnet 41, the magnetically attracted armature 42 and connected wiper are also moved to adjust the potentiometer and thus the position of the piston in the cylinder is indicated by the remote indicating instrument 40 which is appropriately calibrated.

It will be appreciated that the tubular bore of the piston rod 27 must be of sufficient length to accommodate the length of the tube 28 when the ram is in its fully retracted condition.

The tube 28 may be of copper, brass, stainless steel or some other non-magnetic material and must be capable of withstanding the full pressure applied to the ram. If the tube is not strong enough itself then it may, for example, be filled with a non-conducting liquid such as a transformer oil and sealed.

When sufficient magnetic coupling can be Obtained through even a thick walled tube 28, the tube can be airfilled at atmospheric pressure and. no special sealing at the terminal connections will be required where they pass through the end of the ram,

The resistance element 30 may be a molded carbon resistance track. Alternatively, a wire-wound potentiometer may be used having a rigid core or in the form of a. spaghetti winding on a flexible glass fibre core.

An alternative to the use of a resistance track is to insulate electrically the inside walls of the tube 28 but not the end closures thereof and to substitute a conductive liquid for the potentiometer track, one of the electrical connections being taken to the armature 42 by an insulated wire and the armature serving as a wiper. In other words, the three electrical connections will be taken one to each of the opposite ends of the tube and the other to the armature. A conductive liquid is selected which is nonelectrolytic and has the right resistance characteristics and is not subject to polarisation. This conductive liquid may be any suitable ionic solution, e.g., an aqueous solution of an acid or salt such as sulphuric acid or sodium chloride Referring now to FIGURE 5 of the drawings, the hy= draulic ram comprises a cylinder 25 and a ram proper having a piston 26 and a piston rod 27 The piston rod 27 is of tubular construction and re= ceives a tube 28 of non-magnetic material, The tube 28 is sealed at both ends so as to isolate its interior from the pressure-fluid in the ram cylinder, the tube being attached at one end to the cylinder head 25a.

Enclosed within the tube 28 are a plurality of resistance elements or resistors 43 connected in series in a cir= cuit comprising the resistance lead 43a and-return leads 43b and 430.

Also enclosed within the tube 28 are a plurality of eapsulated reed switches 44 one such switch being asso ciated with each resistance element 43 to connect a ter= minal, between each successive pair of resistors 43, to the return lead 430. The spring-reed movable contacts 44a of the reed switches 43 have a bias such that the switches are normally in the open condition. The arrangement is such that the combination of resistance elements 43 and reed switches 44 provide a form of step-by-step potentiometer,

Operation of the switches 44 and thereby adjustment of the potentiometer device is eitected, in accordance with the movement of the rams 26, 27, by means of a magnetic coupling comprising a ring magnet 41 secured to the piston. 26 and slidable over and along the exterior of the tube 28. Each reed 44a is adapted to act as an armature or second 4 element of the magnetic coupling so that the switch is closed by the ring magnet 41 as it passes over the switch or comes into its vicinity,

The three potentiometer connections 37 may be connected in a remote indicating system after the manner described with reference to FIGURE 4.

As mentioned above, the chain of resistance elements 43 forms a potentiometer and the switches 44 select tapping points in the chain, thus in effect acting as a potentiometer slider which steps from point to point of the potentiometer instead of sliding therealong in the usual way. The switch or switches 44 which is or are closed will, of course, depend on the position of the piston 26 so that said piston, in effect, controls the fiow of current or potential in the indicator system and the indicating instrument in that system is caused to take up a position which will indicate the movement of the piston 26 along the cylinder 25.

The switches 44 will spring open, due to the natural resilience of the reeds 44a, or otherwise be caused to open (under the influence of light springs, not shown, or gravity) as the piston and magnet 41 move out of their vicinity.

The number of different positions of the piston 26 which the indicating instrument can indicate will, of course, depend on the number of switches 44.

The chain of resistances could be replaced with suitable circuit modifications, by a chain of inductors or capacitors, which like resistors control electric current fiow or conduction. Hence resistors, inductors and capacitors are hereinafter termed electric current conduction control elements.

A disadvantage, in some circumstances, of the reed switch operated potentiometer system described with ref erence to FIGURE 5 is that after the magnet 41 has passed the reed switches will open and a reading of ram position will only be given when the ram head 26 is actually close enough to a reed switch to operate it.

FIGURES 6, 7 and 8 show alternative arrangements by which this disadvantage may be overcome. In certain respects the arrangements shown in FIGURES 6, 7 and 8 are similar to that shown in FIGURE 5 where applicable like reference numerals have been used to designate like parts. The resistances associated with the switches 44 are not shown in FIGURES 6, 7 and 8.

In the embodiment shown in FIGURE 6 each magnetic reed switch 44 has a short bar magnet 45 at one end and either another magnet or an iron pole piece 46 at the other, so arranged that there is a large gap 47 between the ends furthest from the switch, said ends being close to the stainless steel tube 28. There is no magnet in the ram head 26.

The switches 44 are operated by the steel ram proper 26, 27 of the ram decreasing the reluctance of the magnet path round the magnetic circuit formed by the bar magnet 45, the pole piece 46 and the magnetic reed switch 44. The ram proper 26, 27 closes the magnetic circuits to passage of sufiicient magnetic flux to close and maintain closed all the switches 44 which happen to be within its tubular bore,

In the embodiment shown in FIGURE 7 a bar magnet 48 is fixed parallel with each magnetic reed switch 44 and just close enough to operate it. Here again, there is no magnet in the ram head 26,

When the ram proper 26, 27 comes near to a magnet 48 which is fixed as close as possible to the wall of the stainless steel tube 28, a large proportion of its total flux is shunted by steel ram proper leaving insufiicient. flux to keep the reed switch 44 closed. When the ram proper moves away from the magnet the reed switch re-closes as the flux returns to its path through the reed switch. Thus, all the switches within the tubular bore of the ram proper are maintained open and all those outside said bore are closed,

In the embodiment shown in FIGURE 8 a magnet 41 is housed in the ram head 26. Each reed switch 44 has a short tube 49 of non-magnetic material. alongside it as shown. In the tube is a short 'bar magnet 50 about half the length of the tube and free to slide axially. At each end off the tube 49 a small iron stud 51 is'fixed so that the magnet tends to stay at whichever end of the tube it is put. I

The position of each tube 49 is such that when its magnet 50 is at one end of the tube the reed switch 44, associated witli that tube, is closed by passage of flux through the switching element and when it is at the other end the reed switch is opened by its natural resiliency or by means not shown.

The magnet 41 in the ram head 26 is sufiiciently powerful to overcome the latching effect between a magnet 50 and the iron studs 51 at the ends of its tube 49 so that as the ram head passes each tube magnet reed switch assembl y -49, 50, 44, from left to right in" FIGURE 8, the magnet 50 is moved to the right-hand end of the tube and operates the reed switch keeping it closed after the ram head has passed. When the ram head passes in the other direction the magnet 50 is moved to the left-hand end of its tube where it no longer affects the reed switch, and the switch opens.

The power of the magnet 41 in the ram head need not be closely controlled as it need only be powerful enough to pick up each bar magnet 51 as it passes.

None of the embodiments described with reference to FIGURES 6, 7 and 8 gives a potentiometerputput so that the ram position must be read as a change in resistance of the circuit, each reed switch being arranged (see FIG- URE 9) to short out a section of a chain'of resistors 43 connected in series. This change in resistance is utilized in a system similar to that shown in FIGURE 4 to operate the remote indicating instrument.

FIGURE 10 shows an embodiment similar, in some respects, to that described with reference to FIGURES 2, 3 and 4, but having an alternative to the slider and moulded track or Wire-wound rectilinear potentiometer 30-34. In this embodiment there is still a magnet 41 in the ram head 26 embracing a stainless steel tube 28 attached to the cylinder 25.

Insteadof the tube 28 housing a rigid rectilinear potentiometer, the inside Walls of the tube are insulated by a non-conducting lining 52 and the tube is filled with a conducting liquid, such as an aqueous solution of sulphuric acid or sodium chloride. Connections are made to the conducting liquid at the ends of thetube through electrodes 53 and 54 immersed in the liquid, "and a further electrode-{55 situated within the tube 52Iis electrically connected to a terminal extending outside of the tube via an insulated flexible wire 56 The third electrode 55, which forms the potentiometer wiper," is of magnetic material or is attached to a piece of magnetic material, and the insulated wire 56, to the end of which it is connected, is 'sufliciently long and flexible to allow the wiper to travel along the length of the tube. The wire 56 may be coiled into a spring.

The magnet 41, in passing along the outside of the tube 28 will draw the wiper electrode 55 through the liquid and the device will operate as a potentiometer. The fact that the tube 28 is filled with liquid makes it possible to use light gauge material for the tube 28 without danger of collapse through external pressure.

It will be understood that a hydraulic prop (e.g. such as is shown in FIGURE 1) incorporating the present invention may be similar in construction to the rams above described and shown in the drawings, a main difference being that a prop will be arranged to stand on its end.

Transducers as above described are very suitable as roof support hydraulic prop or ram extension transducers as they can be made thin enough to fit inside a prop or ram without introducing serious mechanical problems.

It may be possible to make a transducer assembly no greater than inch diameter particularly when using 6 the arrangement described with reference to FIGURES 8 and 10.

I claim:

1. A self-advancing mine roof support having a hydraulic ram member for advancing it and at least one hydraulically extensible prop member for securing it between floor and roof, at least one of said members being combined with means for indicating its extension and retraction comprising a cylinder, a piston within said cylinder, means for entry and exit of a pressure-fluid to and from the cylinder, at least one electric current conduction control elemeiit within said cylinder, means isolating said control element from pressure-fluid within the cylinder, means for varying the current conduction of said control element, and magnetic means responsive to relative movement of saidrpiston and cylinder to adjust said control element varying means.

2. A self-advancing mine roof support as claimed in claim 1 wherein the electric current conduction control element comprises a plurality of resistors connected in series between terminals adapted to be connected to a power source, the means for varying the conduction of the control element being a plurality of switches one connected between each adjacent pair of resistors so as to alter the number of resistors connected to said terminals when a switch is operated, the means responsive to relative movement of the piston and cylinder so as to actuate said switches comprising at least one magnet carried by the piston and operative to close said switches in turn as the piston moves relative to the cylinder.

3. A self-advancing mine roof support as claimed in claim 1 wherein the electric current conduction control element comprises a plurality of resistors connected in series betweeh terminals adapted to be connected to a power source, said means for varying the conduction of the control element being a plurality of switches one connected between each adjacent pair of resistors so as to alter the number of resistors connected to said terminals when a switch is operated, the means responsive to relative movement of said Piston and cylinder so as to actuate said switches comprising at least one magnet disposed adjacent each, switch and operative to close the associated switch until magnetic flux is diverted from the switch by approach of said piston.

4. A self-afdvancing mine roof support as claimed in claim 1 wherein the electric current conduction control element comprises a plurality of resistors connected in series between terminals adapted to be connected to a power source, said meas for varying the conduction of the control element being a plurality of switches one connected between each adjacent pair of resistors so as to alter the number of resistors connected to said terminals when a switch is operated, the means responsive to relative movement of said piston and cylinder so as to actuate said switches comprising at least one magnet disposed adjacent each switch and operative to close the associated switch when magnetic flux is diverted thereto by approach of the piston. 1

5. A self-advancing mine roof support as claimed in claim 1 wherein the electric current conduction control element comprises a plurality of resistors connected in series between terminals adapted to be connected to a said switches comprising at least one magnet slidably dis-' posed adjacent each switch for movement to positions which respectively open and close the associated switclr and an additional magnet secured to the piston for moving said slidable magnet upon approach of said piston.

6. A self-advancing mine roof supportas claimed in claim 1 wherein the electric current conduction control element comprises a body of conducting liquid enclosed 7 8 in an elongated casing of insulating material, a pair of References Cited fixed electrodes Within said casing near opposite ends UNITED STATES PATENTS thereof, a movable electrode of magnetic material within the casing and a magnet mounted in said piston and moV- 1,617,287 2/1927 Huggins Q able along said casing with the piston to cause movement 5 1,723,172 8/1929 Hugglns -340193 of aid movable glectrode 2,620,661 Roux 73 3 7. A self-advancing mine roof support as claimed in 2,828,481 3/1958 Lataple 340-282X claim 5 wherein magnetic latching means is provided to 3,200,645 8/1965 Levms 73 313 retain said slidable magnets in their switch open and 3,217,307 11/1965 Fogelqmst 340 188 3,341,843 9/1967 Walsh 340421 closed positions after having been actuated thereto by 10 movement of the piston in one direction until positively JOHN W CALDWELL Primary Examiner moved to their other position by movement of the piston in the other direction. D. L. TRAFTON, Assistant Examiner, 

